Balloon catheters for the angioplasty treatment of stenosis within the human body circulatory system have been known for a long time. These catheters comprise a balloon at the distal end thereof. The balloon catheter is inserted within the blood vessels with the balloon in a deflated configuration and is brought proximate to the site of stenosis. At this point, the balloon is inflated for a relatively short time span to obtain the dilation of the vessel and concomitantly a mechanical treatment of the stenosis, which is suitable to restore the section of the blood vessel. However, this mechanical action may cause in some patients, at the site of intervention, a cell hyperproliferation known as restenosis, which may again lead to an obstruction of the blood vessel and to severe consequences to the patient.
It has been recently noted that the outcome of a conventional mechanical angioplasty intervention results to be dramatically improved when a drug suitable to prevent restenosis is used in association therewith. Suitable drugs for this kind of treatment are antiproliferative drugs. These drugs can be, for example: rapamycin, epothilone and mainly paclitaxel.
Attempts have already been made to coat the angioplasty balloon with a gelatinous layer consisting of a mixture of a suitable solvent and paclitaxel. Patent applications WO 2004/028610, WO 2004/028582, and WO 2002/076509 to Ulrich Speck describe the positioning of a lipophilic drug, such as paclitaxel, on the outer portion of an angioplasty balloon.
This known method, however, is not without defects.
In fact, in order to reach the site of stenosis, the balloon catheter is required to travel along a relatively long pathway within the healthy blood vessels, while being exposed to the blood stream. Along this pathway, the drug, even if lipophilic, is very likely to be partially removed from the balloon due to friction against the vessel walls or to the flushing and rinsing effect of the blood flow.
This at least partial removal of drug from the balloon determines some undesirable consequences. Firstly, the administration of the drug to the stenosis area is lower than expected and a priori unknown. Secondly, an amount of the drug is dispersed in unintended districts of the body, with consequent undesirable secondary effects due to the intrinsic toxicity of the antiproliferative drug that is used.
Moreover, it has been observed that after the drug has been carried close to the stenosis, it can immediately be lost after the normal blood flow has been restored.
An angioplasty balloon catheter that comprises a chamber between the folds filled with a drug is known. It has been observed however that, when immersed into a blood environment, this type of balloon may partially lose an amount of drug before reaching the final destination, as the folds tend to open or the plasma tends to reach the cavity under the folds by capillarity.